Gas turbines operate under extreme conditions. In order to drive efficiency higher, there have been continual developments to allow operation of gas turbines at ever higher temperatures. As the temperature of the hot gas path increases, the temperature of adjacent regions of the gas turbine necessarily increase in temperature, due to thermal conduction from the hot gas path.
In order to allow higher temperature operation, some gas turbine components, such as nozzles and shrouds, have been divided such that the higher temperature regions (such as the fairings of the nozzles and the inner shrouds of the shrouds) may be formed from materials, such as ceramic matrix composites, which are especially suited to operation at extreme temperatures, whereas the lower temperature regions (such as the outside and inside walls of the nozzles and the outer shrouds of the shrouds) are made from other materials which are less suited for operation at the higher temperatures, but which may be more economical to produce and service.
Joining the portions of gas turbines in higher temperature regions to the portions of gas turbines in lower temperature regions may present challenges, particularly with regard to interfaces between metals and ceramic matrix composite materials. Large thermal gradients between the metal portion and the ceramic matrix composite portion may result in high thermal strain in the component, reducing performance and component service life. Further, in many instances, components having a metal portion and a ceramic matrix composite portion include a volume between metal and ceramic matrix composite portions for which a flow of a purge gas is appropriate. Purge gas may be used, among other purposes, to minimize leaks between adjacent turbine components. However, providing both a purge fluid to purge the volume between the metal and the ceramic matrix composite portions as well as a temperature modulation fluid to reduce temperature differentials and thermal strain across the interface between the metal portion and the ceramic matrix composite portion may reduce the efficiency of the turbine by requiring a greater flow of fluid to be diverted from the compressor than either a purge fluid or a temperature modulation fluid would alone.